"In previous studies, it has been found to be useful in detecting the residues of explosives found on luggage,” said R. Graham Cooks, the Henry Bohn Hass Distinguished Professor of Analytical Chemistry in Purdue's College of Science. While ordinary mass spectrometry is both time- and labor-intensive, the Cooks team has modified the devices so that not only are they portable enough to be carried in backpacks, but they can also determine the chemical composition of an unprepared sample within five seconds.

Their modified spectrometric technique, which the team has dubbed desorption electrospray ionization (DESI), involves aiming a fine water mist at a surface with a pencil-sized tube that also sucks up the fluid after the droplets have mixed with the material in the sample.

DESI can detect certain telltale chemicals that are present at abnormal levels. "We see DESI as a microscope that can 'see' chemicals instead of light. As we move the 'wand' across tissue, it can reveal what chemicals are where, and these chemical signatures are clues to what's happening in the body," said Takáts, a postdoctoral assistant in Cooks' lab. So DESI analyzes tissue in live patients in real time. It can now resolve chemical differences between areas of a sample as small as a half-millimeter, or 500 micrometers. With further improvements, it could resolve objects as small as 50 micrometers, or the size of individual cells.

Cooks said: "Traditional mass spectrometry has been only good at detecting disease markers such as proteins, but DESI has the ability to read the lipids. While analyzing a sample of liver tissue with DESI, the team found that a cancerous region possessed higher levels of certain lipid molecules. The findings could indicate a significant relationship between these fatty substances and tumor proliferation.